Many situations arise where it is necessary to tap fluid into or out of veins or arteries. To do so and for example, during conventional intravenous feeding it may be necessary to inject and withdraw a needle several times. Normally such a procedure requires repeated percutaneous needling of the skin. Further, a patient requiring hemodialysis would need many such needlings. Thus a significant drawback in hemodialysis as is presently practiced is the fact that communication with the appropriate veins must be maintained for repeated periods of short durations over what may be the life of the patient. It is readily apparent that there are significant drawbacks associated with this approach. Not the least of these is the fact that continued reinsertion and breaking of the skin leads to the scarring thereof, causes a "blueing" of the skin on that body portion adjacent the punctures leaving the patient prone to bacterial infection. Further still, continued repuncturing of the skin is painful and may have adverse psychological consequences.
Several approaches are currently utilized to provide vascular access during hemodialysis. In one approach, two needles are inserted into the patient's veins wherein the needles are coupled to an appropriate artery by means of a fistula. An advance over this method utilizes a single needle approach and a phase-shift pressure regulator pumping system for dialysis. While this last mentioned single needle approach is an improvement over the two needle scheme, it still requires continued percutaneous needling of the skin and dilated veins each time the patient is dialysised.